The present invention relates to a disc driving device for carrying out recording and/or reproducing of information to a disc-shaped information recording medium, and more particularly to a disc driving device having a carriage moving device with an improved intermittent feeding mechanism.
In a disc driving device for carrying out recording and/or reproducing of information to an information recording medium, it is necessary to move a magnetic head for writing and/or reading a signal in a radial direction of the recording medium. A moving device for moving the magnetic head requires to be equipped with a motor as a driving source and a transmitting mechanism for transmitting a driving power of the motor to a carriage supporting the magnetic head.
A conventional disc driving device having such a moving device as above is disclosed in Japanese Patent Application No. 61-52357 filed by the same applicant as in the present application. The disc driving device disclosed in the preferred embodiment of the prior art is a so-called still video floppy device for recording/reproducing a still picture. The constitution of the still video floppy device will be described below with reference to FIGS. 5 to 8.
Referring to FIGS. 5 to 8, the disc driving device includes a frame 1; a slide plate 2 slidable on the upper surface of the frame 1 in the vertical direction as viewed in FIG. 5; a holder 7 for holding a disc cartridge, having side projections 6a and 6b to be engaged with cam grooves of side plates 2a and 2b of the slide plate 2 adjacent to side plates 3 and 4 of the frame 1; a motor 9 mounted on the upper surface of the frame 1 for rotating a turn table 8; the motor 9 and the turn table 8 constituting a disc driving mechanism; a carriage 10 provided on the upper surface of the frame 1 and adapted to be moved in a radial direction of a disc; a carriage moving mechanism 12 for moving the carriage 10 by a stepping motor 11; and a lock lever 14 adapted to limit a slide position of the slide plate 2.
The carriage moving mechanism 12 used in the disc driving device is assembled to form a carriage moving unit 20. Referring to FIGS. 7 and 8, the carriage moving unit 20 is primarily constructed by a support plate 21, the stepping motor 11 and a screw shaft 22. The support plate 21 is bent to form upper and lower stages as is apparent from FIG. 7. A stepping motor mounting portion 23 is formed at the upper stage, and the stepping motor 11 is mounted on the lower surface of the stepping motor mounting portion 23. The screw shaft 22 is supported by bearings 26 and 27 supported to both side walls 24 and 25 of the carriage moving unit 20. The screw shaft 22 and the stepping motor 11 are assembled with the support plate 21 to form a unit.
An intermittent driving screw 28 formed on the screw shaft 22 is similar to that disclosed in Japanese Laid-Open Utility Model Publication No. 60-67564 filed by the same applicant as in this application. Referring to FIGS. 9 to 11, a plurality of groove portions 22a are formed on the outer circumference of the screw shaft 22 in a predetermined axial range. Each of the groove portions 22a is parallel to a perpendicular Y at right angles to an axia X, that is, has a lead angle (=.theta..sub.2) of zero, and is straight at its bottom. The groove portions 22a are arranged in such a manner as to be sequentially shifted in the axial direction of the shaft 22, thereby forming a spiral groove 22b. At a connecting portion between the adjacent groove portions 22a, there is formed a feeding portion 22c for feeding the carriage 10 at a predetermined pitch.
In the carriage moving unit 20 as mentioned above wherein the engagement member 29 of the carriage 10 is engaged with the spiral groove (intermittent driving screw) 22b of the screw shaft 22, when the engagement member 29 is slided in the feeding portion 22c of the spiral groove 22b by the rotation of the screw shaft 22, the carriage 10 is moved in a predetermined direction according to a lead angle .theta..sub.1. Furthermore, when the engagement member 29 comes to the target groove portion 22a of the spiral groove 22b, supply of current to the stepping motor 11 is cut to stop the movement of the carriage 10. Thus, the engagement member 29 is moved in the feeding portion 22c, and is stopped at the target groove portion 22a to thereby carry out intermittent feed of the carriage 10. Since the lead angle .theta..sub.2 in the groove portions 22a is zero, a stop position of the carriage 10 may be properly set to increase the accuracy of the stop position even if a rotary angle of the screw shaft 22 is slightly slipped.
Bearings 26 and 27 for supporting both the ends of the screw shaft 22 are pivot bearings to rotatably support the conical ends of the screw shaft 22. As shown in FIG. 8, on the bearing 26 side, the screw shaft 22 is rightwardly biased by a compression spring 30, while on the bearing 27 side, an axial position of the screw shaft 22 is adjustable by means of an adjusting screw 31. The bearing 27 is supported to the side wall 25 as mentioned above, and the end 32 of the bearing 27 is projected from the side wall 25. The projected end 32 is inserted into a support hole 33 of the side plate 4 of the frame 1 to define a vertical position of the carriage moving unit 20 itself.
A spur gear 34 mounted to the screw shaft 22 is meshed with the crown gear 36 mounted to a rotating shaft 35 of the stepping motor 11 mounted to the support plate 21 to transmit a step operation of the stepping motor 11 through the crown gear 36 and the spur gear 35 to the screw shaft 22. Thus, the rotational operation of the stepping motor 11 is transmitted through the intermittent driving screw 28 to the carriage 10 to advance the same every step.
In the disc driving device as mentioned above, a track space of a magnetic disc (not shown), e.g., a still video floppy disc is 100 .mu.m, and a maximum amount of off-tracking of the disc driving device is specified to .+-.15 .mu.m. This value is specified in consideration of compatibility of the disc in a reproducing apparatus. The amount of off-tracking in this range would not hinder usual reproduction in outline. However, a picture quality is remarkably improved by finely adjusting a head position in the reproducing apparatus according to the amount of off-tracking.
In the above disc driving device, fine adjustment of the position of the magnetic head 37 is effected by the adjusting screw 31. When the head position is finely adjusted to an optimum position upon reproducing, and recording is carried out under the condition, the recording process is effected under the reproducing off-tracking condition. When the recorded picture is reproduced by another reproducing apparatus, a head position of the reproducing apparatus is required to be finely adjusted again to the specified amount of off-tracking. Then, in the case of recording a picture by the disc driving device used for reproduction, and reproducing the picture recorded by a still another reproducing apparatus, the fine adjustment is required similarly. In this manner, the fine adjustment is accumulated to cause an accumulated amount of off-tracking. As a result, the amount of off-tracking cannot be covered by the prescribed range of .+-.15 .mu.m to cause a possibility of hindrance of compatibility of the disc.
To cope with this problem, it is necessary to always maintain a normal track position upon recording and conduct the fine adjustment upon reproducing only, and especially upon reproducing a picture recorded by another disc driving device. In other words, it is necessary to provide a servo mechanism for always returning the magnetic head to a predetermined recording position upon recording irrespective of the fine adjustment upon reproducing and for maintaining an optimum position upon reproducing.
The servo mechanism is operated to move the screw shaft 22 itself in its thrust direction. However, the provision of the servo mechanism makes the disc driving device complicated to cause an enlarged size of the device and an increased cost.